In the past there have been numerous efforts made to develop controlled release or sustained release pesticides. One approach has been to entrap the pesticide in a protective polymeric coating such as, for example, the methods described in U.S. Pat. No. 3,569,769 and U.S. Pat. No. 3,269,900. Another approach has been to chemically couple the pesticide directly to a natural polymeric substrate such as lignin as described in Canadian Pat. No. 863,310 and still another approach has been to use a bridging compound to connect the pesticide to the natural polymeric substrate such as that described in Canadian Pat. No. 855,181. In addition, pesticides have been dissolved in waxes, incorporated in emulsions and combined with large amounts of inert carriers all in an effort to obtain sustained released pesticide compositions.
None of the above described approaches is completely without disadvantages. For example, entrapping the pesticide in a polymer is relatively expensive; the use of a natural polymer substrate may result in a product which is not only of a nonuniform consistency from batch to batch, but which is also bulky to transport and handle and the incorporation of pesticides in emulsions, waxes, and compositions including inert carriers may result in non-release or uneven release of the active ingredient.